1. Field to which invention relates
The present invention relates to glass refining.
2. The prior art
It is known that the surface layer in a glass tank differs in respect of its chemical composition from the layers lying underneath it. The change in the chemical composition is due to the fact that some components of the glass react with the furnace atmosphere and/or evaporate and escape. As a rule therefore the surface layer has a higher silicic acid content. Sometimes also bubbles and/or foam may be produced. These surface layers can lead to difficulties in processing the glass to produce the finished product, and to more or less pronounced streaks in the finished product. In order to avoid these consequences, the prior art method provides for separating the surface layer of the fused glass from the main flow and the separated surface layer is then diverted and removed from the prehearth of the fusing tank. Such a method is described in the German Patent specification (Offenlegungsschrift) 2,106,061.
For certain purposes particularly high requirements are raised as regards the homogeneity of the glass which comes to be processed and these requirements cannot be satisfied with the prior art method. This is always the case when glass articles or products are to be produced with a high optical quality, for example a transparent glass strip with plane parallel surfaces. It is just in the case of such glass strips, which are produced today in accordance with the drawing method or in accordance with the float method, that such division up into layers and streak formation can lead to a disadvantageous effect in the glass. However, also in the case of the production of other articles as for example the production of articles of glass compositions with a high melting point, of colored glass, in the case of the production of hollow glasses etc. the homogenization of the glass melt can present a substantial problem so that in this case as well there is also a requirement for a method with which it is possible to produce extremely homogeneous glass melts.